The present disclosure relates generally to methods and systems for the formation of catalyst slurry for eventual introduction into a polymerization reactor. More particularly, the presently disclosed systems and methods relate to techniques for increasing the activity, reliability, consistency and predictability of chromium-based olefin polymerization catalysts.
This section is intended to introduce the reader to aspects of art that may be related to aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
As methods, processes, and equipment within chemical and petrochemical technologies advance, the higher-quality, lower cost materials and products that result become more and more prolific in our everyday lives. In particular, simple molecular building blocks (or monomers) may be brought together into longer chains (or polymers), through a chemical process called polymerization to yield these materials.
Polyolefins, a type of polymer widely consumed on an everyday basis, may be produced from various olefin monomers and additives. In typical polyolefin reaction processes, various components are added to a polymerization reactor to begin the polyolefin reaction process. These various components can include olefin feed components, diluent components, additives, and catalyst components. Upon introduction of the various components into a polymerization reactor, the polymerization reaction process begins. The polymerization reaction takes place within the polymerization reactor under a given set of reaction conditions. The controlled or measured reaction conditions within the polymerization reactor can include reaction temperature, reaction pressure, reactor residence time, and concentrations of the various components within the reactor, such as reactor solids, ethylene, hexene, hydrogen, co-catalysts, antistatic agents, electron donors, and inerts, such as ethane and propane.
In addition to the monomers that may be used, the variable reaction conditions under which the polymerization occurs may affect the various physical and mechanical properties of the obtained polyolefin. Depending upon the application and market in which the polyolefin is to be used, some physical properties that can be desired, depending on the product requirement and application, are molecular weight, molecular weight distribution, density, crystallinity, and rheology. Some mechanical properties that can be desired, depending on the product requirement and application, are modulus, tensile properties, impact properties, stress relaxation, creep, and elongation. Despite advances within polymerization technologies over the past few decades, consistently obtaining polyolefins with specific properties remains a difficult task, as precise control over polymerization reaction variables is among the more difficult hurdles associated with polyolefin production.
In conventional polyethylene loop reaction processes, the dry, solid catalyst is combined with olefin-free diluent in an unagitated vessel known as a mud chamber. The catalyst settles to form a catalyst mud, which is then directed to the polymerization reactor by a ball-check feeder system. Feed lines are directed into the polymerization reactor for the introduction of other reactor components including activators, dessicants, reducing agents, diluents, and the like. The other polymerization components are introduced directly into the reactor and are monitored using separate gauges, pumps, and dilution tanks for each.
Additionally, as various feed streams are introduced directly into the polymerization reactor, activating agents, reducing agents, newly formed catalyst poisons, and the like can be locally concentrated at the site of introduction. This may create local inhomogeneities in activity and random pockets of heating within the reactor. Within these local areas, unwanted side processes may occur which could have a significant negative impact on the overall performance of the reactor and the properties of the resultant polymer.